The present invention is directed to the field of packaging. More specifically it deals with carbon dioxide releasing systems in conjunction with systems capable of absorbing oxygen. Bag and sachets incorporating such components are also discussed. Modified packages associated with the use of such systems are also discussed as are methods of use associated with the present invention.
The description of the present invention will be discussed predominantly in relation to meat products whose associated packaging problems are typical of those which the present invention considers. However it should be appreciated that the present invention can also be applied to other foodstuffs and articles to be packaged.
More specifically, and for simplicity of description, the problems associated with chilled and fresh meat will be discussed as the problems associated with these products are perhaps the most demanding. Consumer perception is that a red meat product is a fresh meat product and therefore preferable to discoloured products. Unfortunately, for fresh and chilled meats, storage under conditions where oxygen is present results in gradual browning of the meat. While in many cases (short term storage) the product is still acceptable, the consumer is deterred by the brownish appearance of the meat which they associate with a spoiled product.
Where there is longer term storage of meat products, the presence of oxygen can result in not only the browning of the meat but subsequent spoilage. Accordingly packages for long term storage of meat generally comprise an oxygen impermeable barrier film. Often the packages are evacuated or packed under a modified atmosphere.
Vacuum packaging is not generally considered appropriate for the retail display of chilled red meat, because of the meat""s purple coloration. Low oxygen modified atmosphere systems are also not appropriate for the same reasons.
High oxygen/low carbon dioxide modified atmosphere systems are successfully used for retail cuts of red meat, but in this case, the storage life is low due to oxygen spoilage.
Recently a packaging system known as low oxygen/high carbon dioxide packaging has become very popular. The system has been directed mainly at non-retail ready markets, as the primal cuts used require further processing into consumer portions. Also the next requires re-exposure to oxygen to resume a red rather than purple colouration.
It has been found that chilled meat packaged under carbon dioxide is resistant to spoilage by aerobic bacteria. Anaerobic bacteria which may still survive under Carbon dioxide do not flourish below 2xc2x0 C., which is above the storage temperature of most chilled meat products. Evidence suggests that a relatively high concentration of carbon dioxide will actively suppress the bacterial growthxe2x80x94the shelf life of Carbon dioxide packaged meat is thus much longer than for vacuum packed meat.
Like the vacuum packed product, meat stored under carbon dioxide will rebloom on exposure to oxygen, giving the red coloration which consumers associate with freshness. However, it is also believed that the display life, in the oxygenated state, of carbon dioxide packaged meat is longer than that of vacuum packed meat. This may be associated with the low oxygen concentration throughout the product lifetime, which is a key requirement of the carbon dioxide process.
The use of low oxygen/high carbon dioxide packaging is well known, as is the use of oxygen absorbing compositions with meat products. Combinations of the two systems are also known. However, many problems remain.
For instance systems which release carbon dioxide are well known. Of note is the work of Benedict, Strange, Palumbo and Swift (Journal of Agricultural and Food Chemistry, 23 (6) 1202-1208 1975). Gas permeable sachets consisting of citric acid and sodium bicarbonate were added to retail package of meat and the carbon dioxide released helped to extend shelf life. Codimer also patented a system where carbon dioxide and/or oxygen were generated in a package from the reaction of citric acid with sodium bicarbonate and/or sodium perborate (EP O 128 795 (1984)).
A number of other systems also appear in the prior art which both absorb oxygen and liberate carbon dioxide. These systems were designed to replace the oxygen absorbed from within the head space of the package with high levels of carbon dioxide. For example, Toppan claims highly specific compositions such as:
100 parts ferrous chloride
20-100 parts sodium bicarbonate
5-50 parts water supplying substance
0-10 parts absorbent
0-70 parts iron powder
No examples or disclosure is provided within this patent which produce large amounts of carbon dioxide and absorb small amounts of oxygen (U.S. Pat. No. 4,384,972 (1983)).
Mitsubishi described a system where the amount of carbon dioxide generated may be independent of the amount of oxygen absorbed. However the teaching of this specification limits the amount of carbon dioxide produced per mole of oxygen absorbed (U.S. Pat. No. 4,726,722 (1988)).
However the prior art fails to address the problems associated with the packaging of meat, and especially the packaging of meat in retail ready tray-based packages. The Mitsubishi system was intended to be used for sealing a package without evacuation or gas flushing and in its place greater than two moles of carbon dioxide per mole of oxygen absorbed was said to lead to pack deformation. At the time of this patent the prior art also considered that carbon dioxide gas flushing when packaging meat resulted in unwanted browning. Accordingly the art considered, and this is reflected in the limitations of the art, the excessive carbon dioxide, such as would also result through carbon dioxide gas flushing, was undesirable. However it has since been found that this browning is not due to carbon dioxide but rather to the incomplete removal of oxygen from within the package and may be a temporary condition, depending upon the levels of enzyme activity which relates to time post mortem.
Other prior art, such as EP O 527,228 (Toppan) describes oxygen absorbers/carbon dioxide generators such as mixtures of ascorbic acid and ferrous chloride. However the quantity of carbon dioxide released is dependent upon the amount of oxygen absorbed as well as on the pH of the composition. The pH may be determined by the addition of an alkali such as sodium bicarbonate, sodium carbonate of calcium hydroxide. However this disclosure is targeted at applications where a set amount of carbon dioxide and nitrogen is required within a container (e.g. container for growing bacteria samples). This, and the known prior art, fail to address the need of package meat for extended periods of time, and be able to regenerate or preserve a consumer acceptable red colouration at the retail level. In addition, there is a need, for retail ready packs, to prevent deformation of a pack due to variations in the internal atmosphere. These problems arise due to the fact that meat will absorb large quantities of carbon dioxide, generally within the first 48 hours of exposure. As this absorption process proceeds, the internal pressure of a package is reduced, unless there is a sufficient excess of carbon dioxide to completely saturate the meat, and there is a suitable mechanism by which the volume of the package may contract.
If meat is placed on a conventional sized tray, evacuated, gas flushed with carbon dioxide and the sealed under a barrier film, severe distortion will occur as the carbon dioxide is absorbed and the internal pressure of the system is reduced. This is because the volume of the tray cannot contract in a controlled manner like that of a bag, and because insufficient carbon dioxide is present to compensate for what is absorbed by the meat.
This problem becomes more noticeable as an attempt is made to keep a high product volume in relation to the volume of the package. High product to package volume systems are used conventionally (i.e. PVC overwrapped product on an expanded polystryene tray) for retail display of meat cuts.
Large volume packages containing a low volume of product are resented by consumers, who associate them with excessive packaging and waste. They are also unpopular with retailers as they occupy excessive shelf space, and also with exporters/distributors because of their high volume and low weight.
It would therefore be desirable to provide a system whereby the long storage life and display life of low oxygen/high carbon dioxide packaging could be applied to individual tray or bag wrapped systems, whilst maintaining the low volume associated with the conventional retail meat packaging systems.
It would also be desirable to modify the existing low oxygen/high carbon dioxide packaging in such a manner that the absorption of carbon dioxide by the meat cuts is matched by the generation of carbon dioxide by chemical means. The existing packaging system involves first wrapping the meat cuts in absorbent material, and then placing a number of them in a carton lined with a high barrier bag. The bag is then evacuated, flushed with carbon dioxide and sealed. Frequently the carton is not sealed for a further 24 hours so that most of the carbon dioxide can be absorbed and the final package volume is relatively low. For beef, one liter of carbon dioxide is recommended for each kilo or meat. For lamb, 1.5 liters per kilo is recommended. This delay in sealing the cartons is a source of frustration at the meat plants.
When meat is vacuum packed xe2x80x9cdripxe2x80x9d is drawn to the surface and will accumulate in areas where there is no intimate contact. This detracts from the appearance of the product.
It would also be desirable to extend this concept to a variety of non meat products.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.
According to one aspect of the present invention there is provided a method of packaging for meat in a carbon dioxide rich, oxygen low package environment, comprising the sealing of the meat in an oxygen impermeable package, and including within said package carbon dioxide generating material, and oxygen removing material, the arrangement being such that the production of carbon dioxide is not dependent upon the removal of oxygen. Sufficient carbon dioxide generating material can be included for greater than 2 times the mole ratio of oxygen able to removed by the included oxygen removing material.
According to another aspect of the present invention there is provided a method, substantially as described above, wherein sufficient carbon dioxide generating material is included to release at least 0.1 liter of carbon dioxide, at STP, per kilogram of packaged meat.
According to another aspect of the present invention there is provided a method, substantially as described above, in which sufficient oxygen removing material is included to maintain an oxygen level, within the sealed package of 500 ppm or less throughout the storage life which may be for a period of at least 10 weeks from packaging.
According to another aspect of the present invention there is provided a method, substantially as described above, in which included carbon dioxide producing, and oxygen removing, materials are present in the form of one or more sachets or inserts positioned within the package.
According to another aspect of the present invention there is provided a method, substantially as described above, in which the package contents are separated from the carbon dioxide producing, the oxygen removing materials, by an oxygen and carbon dioxide permeable layer.
According to another aspect of the present invention there is provided a method, substantially as described above, in which the meat is positioned within a tray of an oxygen barrier material, and the tray covered with a oxygen barrier film layer, the carbon dioxide producing and oxygen removing materials being included within the covered tray before sealing.
According to another aspect of the present invention there is provided a method, substantially as described above, in which there is present an oxygen barrier seal overlying an oxygen permeable portion of the package, the removal of which allows permeation of oxygen through the oxygen barrier or impermeable layer.
According to a another aspect of the present invention there is provided a package comprising a tray or bag or other packet, a foodstuff or other item or material within the packet, an atmosphere modifying insert or inserts including carbon dioxide generating material and an oxygen removing material which are both characterised such that the production of carbon dioxide is not dependent upon removal of oxygen.
According to a further aspect of the present invention there is provided a package of meat comprising an outer oxygen impermeable package, there being included within same carbon dioxide generating material, and oxygen removing material which are both characterised such that the production of carbon dioxide is not dependent upon the removal of oxygen, and wherein at the time of packaging sufficient carbon dioxide generating material is included for greater than 2 times the mole ratio of oxygen able to removed by the included oxygen removing material.
According to another aspect of the present invention there is provided a package, substantially as described above, in which the outer oxygen impermeable package comprises an oxygen impermeable tray into which meat is placed and an overlying oxygen barrier film sealing the mouth of the tray, there being included within the package carbon dioxide generating material, and oxygen removing material, the arrangement being such that the production of carbon dioxide is not dependent upon the removal of oxygen.
According to another aspect of the present invention there is provided a package, substantially as described above, comprising an inner sealed oxygen and carbon dioxide permeable packet into which meat is sealed, positioned within an outer oxygen impermeable bag.
According to another aspect of the present invention there is provided an atmosphere modifying insert for maintaining a low oxygen, carbon dioxide rich atmosphere in a package for meat, said insert containing:
a carbon dioxide producing system, and
an oxygen removing system;
the arrangement being further characterised in that the production of carbon dioxide is not dependent upon the removal of oxygen, and wherein sufficient carbon dioxide generating material is included for greater than 2 times the mole ratio of oxygen able to removed by the included oxygen removing material.
According to another aspect of the present invention there is provided an insert, substantially as described above, in which the carbon dioxide envolving system is initiated by the presence of moisture.
A problem with foodstuffs such as meat is that they can absorb large quantities of carbon dioxide. This can cause problems with packaging, and particularly the buckling of retail ready packs due to reduced internal pressure resulting from carbon dioxide absorption. Some other problems have been mentioned previously. One aspect of the present invention seeks to solve this problem by including within the package means for producing a relatively large volume of carbon dioxide while at the same time allowing for the absorption of residual oxygen from packaging, and preferably also any oxygen which permeates into the package throughout its normal lifetime. This may be addressed by including within the package means of generating carbon dioxide and absorbing oxygen. Ideally the amount of carbon dioxide generated is independent of the amount of oxygen-absorbed. Generally also, substantially greater carbon dioxide generating capacity is provided for than oxygen removal capacity. In preferred embodiments sufficient materials are included to generate more than two moles of carbon dioxide for each mole of oxygen able to be absorbed. In many cases preferred embodiments will comprise much higher ratios.
Most embodiments of the present invention will involve the use of means for liberating or evolving carbon dioxide within a package of articles, and in many instances will rely upon a chemical component or system which is able to release carbon dioxide over a period of time. The generation of carbon dioxide within the package can address the problems associated with its absorption by meat or other articles. It is envisaged that in most cases the package will be flushed or sealed under carbon dioxide during packaging. The carbon dioxide generated within the package is generally to counteract absorption by the meat or other articlesxe2x80x94an equally serious problem would be over inflation which ruptured seals of the package. Through this internal generation of replacement carbon dioxide for that which is absorbed, curling of trays (for instance) can be minimised if not totally eliminated.
Accordingly it is preferable that carbon dioxide release is relatively slow over a continuing period of time to prevent over inflation of the package and possible release of carbon dioxide through the package material due to an excessive internal pressure. In most cases the rate of carbon dioxide release should approximate to the rate of carbon dioxide absorption by the packaged contents so that an approximate and desired internal pressure within the package is maintained. For most meats the bulk of carbon dioxide absorption will be within the first 24 hours and it may be desirable to tailor carbon dioxide release to occur predominantly over this period. There will often be an advantage in the slow but continued carbon dioxide release over a longer period to compensate for losses of Carbon dioxide permeating through the film.
The rate of carbon dioxide release may be influenced by a variety of methods. For instance, chemical system may be chosen which will, when activated, release carbon dioxide at the approximate rate. Another method is to make the rate of release of carbon dioxide responsive, or triggerable by, some condition within the package of articles. This condition might be the presence of moisture. Alternatively a system responsive to other stimuli could be used. Stimuli may include light or electromagnetic radiation in the visible and/or near visible regions, and/or electromagnetic radiation in other regions such as the RF, microwave, IR, and UV regions.
Another method is to contain the carbon dioxide evolving materials in a bag or container which limits or controls the rate of ingress of materials triggering carbon dioxide release, or to which the rate carbon dioxide release is responsive to. Secondly the bag or container may control the release of Carbon dioxide evolved within the bag or container.
A further method is to use components whose rate of generation or evolution of carbon dioxide are proportional to the internal pressure of the package. Such materials could be relied upon to maintain an approximate and desired internal pressure of carbon dioxide within the package. This could include the use of substances reversibly adsorbing carbon dioxide and these substances may be combined with other carbon dioxide generating systems such as described herein.
In addition to carbon dioxide evolution, it is desirable for there to be components or a system to remove oxygen which may be present in, or enter the package over time. Most embodiments of the present invention will incorporate such components or systems as even oxygen barrier films will allow the ingress of oxygen over a period of time (such as the period for which chilled meat is often stored). In an example to be given later, it will be shown that the absence of any oxygen removing substance or system will, in some cases, result in a higher than optimum level of oxygen being present in the package.
A wide range of oxygen absorbing or adsorbing compounds and systems are known. Whether the oxygen is absorbed or adsorbed or otherwise removed is not particularly relevantxe2x80x94the main aim is to ensure that there is not a level of free oxygen which could adversely affect the contents of the package.
The prior art has also investigated the use of substances and systems which consume free oxygen in a reaction liberating carbon dioxide. While such systems may be included within the present invention, it should be appreciated that such systems should not be relied upon for the sole evolution of carbon dioxide. As the oxygen levels present within a package are relatively low, such systems will be unable to product sufficient carbon dioxide to satisfy initial absorption by the packaged meat or article. Accordingly, such systems would only be useful for providing a perpetual and low volume supply of carbon dioxide during the life of the package (due to the low volumes of oxygen permeating through the package material) and thus higher volume carbon dioxide evolving systems should be relied upon.
The present invention may also include the use of water or moisture absorbing and/or adsorbing substances. This may be useful in the removal of fluids or excess humidity within the package. However, where these are combined with moisture responsive carbon dioxide evolving systems (such as the acid and carbonate systems to be described later), the affinity and capacity for moisture removal should not be such that the carbon dioxide evolution is not triggered by moisture present in the package. In some cases it may be useful to rely upon hygroscopic or deliquescent materials to draw moisture into the package yet allow sufficient moisture to be available for initiating the carbon dioxide evolution process.
The present invention may also include the use of odour absorbing and/or adsorbing components. Such substances are well known and may be incorporated into various compositions and packages according to the present invention e.g. zeolites, activated charcoals, etc.
Various compositions which may be used in various packages have been discussed. Their inclusion into packages may rely upon a variety of techniques.
For instance, according to one preferred aspect of the present invention the various components of the chosen system are incorporated into a bag or sachet. Typically this bag will be formed of a gas permeable but fluid impermeable material. This will allow gases, and usually water vapour, to pass through the walls of the bas is required. However they will prevent moisture, which is likely to be present in the package, from directly contacting the components of the bag or sachet. This will also help prevent contamination of the packaged articles by the components housed within the bag or sachet.
Micro-perforated films are one such material from which a bag may be constructed, or at least partly constructed. Other films and materials may also be relied upon and various apertures or vents to allow the required transfer of gases or vapours through the bag may be relied upon. The use of valve members may also be considered.
A modification is to use an oxygen absorbing polymer for forming the sachet/container. These may provide sufficient oxygen absorbing properties for a typical package. Other parts of a package may be made from such materials. PCT patent application No. WO 94/12590 describes one such material.
As a variation of the bag, a rigid or semi-rigid container may be produced for insertion into a package. This may be substantially inflexible which may make it more difficult to disguise within a package. It could however, conceivably be moulded in a form disguising its presence. An example would be a substantially flat tray insert upon which the meat or articles were placed. Again various valve members, vents or variously permeable portions may be relied upon to allow the necessary flow of gas and vapours.
As a further variation of this concept the components could be housed within a compartment formed into the package or tray. The same options, variations and requirements as for the bag and rigid insert are also appropriate. However a disadvantage of a compartment in an actual package material (e.g. tray) is that for manufacturing simplicity and less problems for the end user, any of the required chemicals and substances are likely to be inserted into the compartment at the time of its manufacture. However it is generally appropriate that the required compositions are included at the time of packaging the meat or articles, depending upon the shelf life of the compositions.
The quantity of composition included is generally proportional to the quantity of meat or other articles to be packaged. Unless the weight and nature of the articles to be packaged are known, it is difficult to anticipate the correct amount of composition to include. Where discrete sachets or inserts are relied upon, one or more can be inserted, as appropriate, at the time of packaging. Alternatively the inclusion of one or more sachets or inserts could be relied upon to supplement the amount contained in any prefilled compartment. It is not generally desirable to have to load free chemicals or substances into a compartment while attempting to package meat or other articles though automatic dispensers could be relied upon to inset appropriate amounts of compositions into packages or compartments.
Bags and sachets for containing various compositions may be formed individually though it is envisaged that strips or sheets of adjacent sachets may be manufactured. Typically the bags will be joined to each other but be separable by pulling or tearing. In some cases cutting may be relied upon though perforations facilitating tearing may be preferred in many instances.
Where the components of carbon dioxide evolving and oxygen removing systems are included in a single package, care must also be taken that the systems and components are compatible. In a preferred embodiment an xe2x80x98organic acid with carbonatexe2x80x99 type system is relied upon for carbon dioxide evolution. The term xe2x80x98carbonatexe2x80x99, as used to describe a component for CO2 evolution, shall also include the xe2x80x98hydrogen carbonatesxe2x80x99 (also known as bicarbonates). A common xe2x80x98organic acid with carbonatexe2x80x99 system of the present invention is citric acid with sodium hydrogen carbonate.
An iron (typically in the form of iron(II) sulphate) catalysed ascorbic acid system is relied upon for oxygen removal from the package. The ascorbic acid can also participate in carbon dioxide evolution though as this is not its preferred role. The resulting ascorbate (from reaction with the carbonate) is still capable of oxygen removal. However, for economy, citric acid will often be the preferred acid for removal dioxide evolution.
While a package according to the present invention may take a variety of forms, including a bag or container, it is envisaged that many retail ready embodiments of the present invention will comprise a tray with a covering film enabling the contents to be displayed in a shelf or refrigerator. The technology associated with such packaging is well known and may be relied upon in implementing such embodiments of the present invention. Technologies associated with other packaging forms which may be used with the present invention are also well known and could also be relied upon.
Modifications, for example to the package, may also be implemented. It has been mentioned previously that after packaging under carbon dioxide, meat will resume a reddish colour if re-exposed to oxygen. Accordingly, it will be necessary to introduce oxygen into the package to allow this reddening to occur. As most embodiments of the invention will have been packaged in a substantially oxygen free environment and with an oxygen impermeable covering, some means must be provided to allow oxygen to enter the package when required.
A physical opening could be created in the package, such as by the retailer breaching the integrity of the container or covering film (e.g. a knife cut, punched hole, etc.), through it is generally preferably that the package remains sealed. This leaves several possible options including the use of operable and closeable valve members to admit air. In other cases, vents which are normally closed may be revealed, perhaps by peeling off a cover layer. Other arrangements to provide a vent between the inside and outside of the package may be relied upon.
Another alternative is to rely upon the presence of an oxygen permeable film which will normally be covered during long term storage of the product under carbon dioxide. One method of use for such a film is to use an oxygen permeable film as a cover layer for the contents and to provide an oxygen impermeable layer overlying this. When it is desired to admit oxygen into the package, the covering barrier layer would be peeled or removed from the package. Such an arrangement need not only be applied as the main viewing window for the container but also in other positions on the package or tray.
A variety of highly permeable inner package could be used in the masterpack concept. One particularly useful style is as follows:
1. Meat is placed in an appropriate tray for retail presentation.
2. It is then lidded with a prepunched permeable film, the punch holes being in approximate positions so that they may be completely covered by a label or other seal at the point of sale. Alternatively lidded trays may be punched in situ on the lidding machine. Partial punch holes may also be formed so that no unwanted material contact the meat.
3. The individual trays of meat with the punched holes are stacked in a barrier bag within a carton. A sachet of the present invention is included.
4. The barrier bag is then evacuated in a chamber machine and gas flushed with sufficient Carbon dioxide to seal the carbon.
At the point of sale of the trays are removed allowing the ingress of oxygen through the punch holes. The trays are then sealed against leakage by the label or other sealant.
The punch holes allow the free circulation of gas which is necessary for efficient evacuation, gas flushing and eventual oxygenation. The labels or seals ensure a drip free container.